Climate Adaptation in the Dutch Delta

Report | 21-03-2012

The Dutch Delta is vulnerable to the possible consequences of climate change, such as sea level rise and higher river discharges. Strengthening the dykes to become ‘unbreachable’ (Delta dykes) may effectively reduce the flooding risks and sensitivity to climate change. Freeing up more fresh water is possible by making adjustments to the New Waterway, where 80% of the Rhine is discharged into the sea, also in extremely dry situations. In this way, fresh water shortages due to climate change may be prevented.

PBL Netherlands Environmental Assessment Agency draws these conclusions in its report ‘Climate Adaptation in the Dutch Delta – Strategic options for a climate-proof development of the Netherlands’. The English publication is an extended summary of the Dutch report that was published on 21 September 2011. PBL has investigated adaptation options for the Netherlands to expected changes in climate and to weather extremes. Which options would be most effective to reduce flood risks? How could freshwater supplies be secured and the climate-resilience of nature and urban areas be improved?

Climate-proofing freshwater supplies requires a more flexible water system and making better use of the water in the Rhine

It is expected that climate change will lead to more frequent and longer periods of water deficit during the summer months. Making better use of the water in the Rhine may compensate for shortages in the freshwater supply. In addition to the option of increasing the water reserves in the IJsselmeer (as previously proposed by the Delta Committee), changes to the management of the New Waterway is an interesting alternative, making more fresh water available. This would be effective because about 80% of all the water in the Rhine is discharged through the New Waterway into the sea – even in dry years – to counteract salt water intrusion. Organising this more effectively, in other words with less water, will release more fresh Rhine water for other uses, such as for irrigation of agricultural land. Moreover, there are various possibilities for making regional water systems more flexible, thus, temporarily curbing demand for water in dry years. The main options are those of optimising water management practices, and water management authorities taking a more flexible approach to salinity standards.

Building unbreachable dykes and managing new development in the Rhine-Meuse floodplain will make the Netherlands safer and more climate-resilient

Flood risk in the Netherlands may be structurally reduced if the Dutch Government acts not only to reduce the probabilities of flooding, but also the possible consequences. An effective way to achieve this is to reinforce the dykes to create so-called Delta Dykes (‘unbreachable dykes’); especially in areas with the highest population densities and concentrations of fixed assets. Building unbreachable dykes will reduce the dangers and impacts of flooding to such an extent that there is little need for adjustment to built-up areas (flood-resilient building) behind these dykes. Because the consequences of flooding are always less damaging when areas are protected by unbreachable dykes, the Netherlands would then also be less sensitive to climate change and unexpected, more extreme weather conditions. In addition, areas must be reserved within the Rhine-Meuse floodplain for managing the consequences of potentially higher river discharges in the future, combined with higher sea levels, in the longer term. This will require management of new spatial developments in the riverine areas.

Climate-proofing ecosystems and biodiversity will require revising the strategy behind the National Ecological Network

Climate change increases the risk of biodiversity loss in the Netherlands. This, in turn, reduces the likelihood of the Netherlands meeting international nature conservation and restoration obligations, in the longer term. Biodiversity levels can be maintained in the face of climate change if nature conservation policies focus more forcefully than at present on increasing the spatial connectivity of nature conservation areas, improving environmental and water conditions, and creating room for natural processes. For the internationally important habitats in the low-lying areas of the Netherlands, this will involve strengthening spatial connectivity in coastal dunes, peat marshes and the Rhine-Meuse floodplain, and restoring natural processes in the Wadden Sea, the south-west delta area and the coastal zone.

Implementation of climate-proofing measures in urban development today may considerably reduce costs for tomorrow

Phenomena associated with climate change, such as urban flooding and water shortages, the retention of heat in built-up areas (heat build-up) and drought, may vary considerably in nature and scale, from city to city and from neighbourhood to neighbourhood. Climate resilience is hardest to achieve in highly urbanised areas. These areas contain the largest proportion of hard surfacing, causing more heat build-up and urban flooding, whereas the space available for mitigating measures is more limited. A broad range of measures is already available for use at various scales, from individual buildings and streets to neighbourhoods, districts and whole cities. Storage and modified sewerage systems could be implemented in new developments. Urban areas are constantly changing; new homes, offices and infrastructure are being built, neighbourhoods and business estates restructured, and sewerage systems replaced. If municipal authorities, developers, housing corporations and private-property owners consistently would incorporate climate resilience into their investments in the built environment and urban facilities, additional costs of climate adaptation could be kept to a minimum. Municipal authorities are most suited to play a leading role in coordinating and managing these adaptations.

A clear division of responsibilities between central government and other parties

Central government has the overall responsibility for tasks such as spatial planning, freshwater supplies and flood protection. In decentralising these responsibilities, central government must create preconditions and enabling mechanisms for municipal authorities, water boards, provincial government and citizens to adapt to climate change, primarily in the areas of urban climate resilience and freshwater supply. This means that central government must provide exact information on the limits to its responsibilities and indicate which investments in climate adaptation it would expect from other government authorities, the business community and citizens.